That's a completely different argument to your original post of:
Some applications make use of multitouch gestures, for which I see no general analog on a mouse. For example, how do I pinch to zoom with a mouse?
I think you're missing the point, a touch screen is just a way of pointing and clicking and requires no extra work to support clicking on a screen with your finger or with a mouse, all of that is handled by the OS. The very few mutli-touch gestures I've seen are also easily supported with a keyboard and mouse. Any good developer writes their application to work with or without multi-touch, look at Google maps again, you want to zoom in but don't have a scroll wheel or a touch screen then use the zoom slider along the side.
You're right of course with your last point, it's possible for a developer to not support certain input devices on purpose. In general they'd have to go out of their way to make an app that doesn't work with a mouse though since touching a spot on a touch screen is the exact same call as clicking a spot on the screen with your mouse. I do have a touch screen on my laptop and while I don't use it because I don't like smudging my screen I can use the screen or the mouse with many applications and those have never been designed specifically to work with a touch screen either. I won't argue the point that it's possible to develop an app that doesn't play well with classic input devices I've seen lots of horribly designed web pages and applications that don't consider usability at all.